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Re: [Qemu-ppc] [PATCH for-2.8 0/3] spapr: fix breakage of memory unplug
From: |
Michael Roth |
Subject: |
Re: [Qemu-ppc] [PATCH for-2.8 0/3] spapr: fix breakage of memory unplug after migration |
Date: |
Fri, 18 Nov 2016 10:39:49 -0600 |
User-agent: |
alot/0.3.6 |
Quoting David Gibson (2016-11-17 23:45:05)
> On Thu, Nov 17, 2016 at 07:40:24PM -0600, Michael Roth wrote:
> > These patches are based on David's ppc-for-2.8 tree, and are also
> > available from:
> >
> > https://github.com/mdroth/qemu/commits/spapr-cas-migration
> >
> > Currently, memory hotplugged to a pseries guest cannot be removed after
> > the guest has been migrated. This is due to 2 issues:
> >
> > 1) The coldplugged state of memory on the target side is one where the
> > corresponding DRC's allocation state is:
> >
> > allocation_state == unallocated,
> > awaiting_allocation == true,
> >
> > When the guest attempts to unplug memory on the target side, it first
> > checks that allocation_state == allocated. If we fix this, the guest
> > can successfully notify QEMU of completion on it's end, but then the
> > DRC code sees that awaiting_allocation == true, so it defers the
> > finalizing of the LMB and corresponding DIMM since it assumes that
> > the DIMM must have been previously allocated before it can be removed.
> >
> > To address this, we pull in patches 1-2 from Jian Jun's DRC migration
> > series:
> >
> > https://lists.gnu.org/archive/html/qemu-ppc/2016-10/msg00048.html
> >
> > with some minor changes relating to prior review comments, and
> > the addition of migrating the DRC's awaiting_allocation value, which
> > wasn't part of the original patch. This doesn't address the full scope
> > of the issues Jian Jun was looking at (involving synchronizing state
> > when migration occurs during fairly small race windows), just this
> > particular case, which is more user visible since the time window is
> > indefinite.
> >
> > 2) The ability to unplug memory is gated on the QEMU side by a check as
> > to whether or not support for newer-style hotplug events was negotiated
> > via CAS during boot. The check is performed by checking the corresponding
> > entry in the sPAPROptionVector structure. However, since this value isn't
> > migrated currently, we are unable to unplug until after the guest
> > reboots.
> >
> > We address that here by adding migration support for sPAPROptionVectors,
> > and including the CAS-negotiated vector as part of the migration stream
> > for any cases where we advertise newer-style hotplug event support to
> > the guest.
> >
> > David,
> >
> > These fixes ended up going out much later than planned. I'm not sure
> > if you're planning another pull for 2.8 or not, and realize there are
> > some patches here not specifically pseries-related so it's
> > understandable if we opt to pursue these for 2.9/2.8.1 instead. But if
> > possible I'm hoping to get these in so that the memory unplug
> > support is fully functional for 2.8.
>
> Yeah, I'm still expecting to push a few bugfixes in before 2.8. So,
> I've merged these patches into ppc-for-2.8 (fixing a couple of trivial
> style nits along the way). I have a couple of comments that I'll make
> on the patches, but they're not important enough to stop these going
> in ASAP.
>
> Unfortunately, of course, this is not the only migration breakage we
> have at the moment. I'm presently wrestling with both breakage due to
> changes in the insns_flags masks, and due to the reworking of the mmio
> windows for the PHB.
Ok, thanks for the heads up. FYI I'm still hoping to get the insns_flags
fix in for 2.7.1 (which is a bit behind at this point, should have schedule
and initial tree posted next week though), so I will keep an eye out for
those.
>
> >
> >
> > hw/core/qdev.c | 6 +++++-
> > hw/ppc/spapr.c | 68
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > hw/ppc/spapr_drc.c | 70
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > hw/ppc/spapr_ovec.c | 12 ++++++++++++
> > hw/ppc/spapr_pci.c | 22 ++++++++++++++++++++++
> > include/hw/ppc/spapr_drc.h | 9 +++++++++
> > include/hw/ppc/spapr_ovec.h | 4 ++++
> > include/hw/qdev-core.h | 9 +++++++++
> > migration/savevm.c | 4 ++--
> > 9 files changed, 201 insertions(+), 3 deletions(-)
> >
>
> --
> David Gibson | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
> | _way_ _around_!
> http://www.ozlabs.org/~dgibson
- Re: [Qemu-ppc] [PATCH for-2.8 2/3] migration: spapr_drc: defined VMStateDescription struct, (continued)